program filip;
type vector=array[1..16] of samllint;
var m,n:vector;
    max:real;
    f,g:text;
    i,j:integer;
    aux_m,aux_n:integer;
begin
assign(f,'filip.in');reset(f);
assign(g,'filip.out');rewrite(g);
max:=0;
readln(f,i,j);
for i:=1 to n do
        for j:=1 to n do
        begin
        readln (m[i]);
        readln (n[j]);
        if m[i]>0 then max:=max + m[i] else max:=max-m[i];
        if n[j]>0 then max:=max + n[j] else max:=max-n[j];
        end;
writeln(g,max);
end.